Electron beams used for radio frequency (RF) power generation are frequently bunched spatially. Examples of devices requiring a spatially bunched electron beam to provide an electomagnetic radiation output because of the relativistic effect of electrons (the negative mass instability of relativistic electrons) are the free electron laser, which provides an optical output, and the gyrotron, which has a microwave output. High frequency RF power sources are of interest to the military for communication and directed energy weapons. Additionally, such a power source is also of interest to the fusion community for electron-cyclotron resonance heating. For example, a high power microwave output could render inoperative local control electronics, such as in a directed missile incorporating a sophisticated guidance system, resulting in loss of the guidance capability. Heretofore, sophisticated electron bunching techniques had to be employed and, in the cases of the free electron laser and gyrotron, components for effecting the bunching of the electrons might be integrated within the already extremely complex traveling wave generation part of the free electron laser or gyrotron.
It is known to heterodyne optical beams. In this technique two collimated optical beams, derived from the same laser source, illuminate a common surface. One beam is the signal beam from the laser and the other beam is frequency shifted relative to the signal beam. One use for optical heterodyning is for optical demodulation. Optical heterodyning can also be used for detection of radiation, Abrams and Gandrud, "Heterodyne Detection of 10.6-.mu.Radiation by Metal-To-Metal Point Contact Diodes", Applied Physics Letters, Vol. 17, No. 4, Aug. 15, 1970.
The generation of a high electron density by thermoemission from irradiating a surface with a laser beam, is also known. For further information concerning the structure and operation of such an electron source, reference may be made to U.S. Pat. No. 4,346,330. An electrical discharge device adapted to switch or attenuate a laser beam is the subject of U.S. Pat. No. 3,912,367. Finally, laser triggering of a high voltage discharge between parallel electrodes is disclosed in U.S. Pat. No. 4,401,920.